1. Field of The Invention
This invention relates to a light source apparatus for providing illuminating light to an endoscope with an imaging element, and to an endoscope system which is related with the observation of a test site by providing illuminating light to an endoscope with an imaging element.
2. Related Art Statement
Currently, endoscope systems for medical applications are widely used among general practitioners. These medical endoscope systems are configured so as to allow one to observe various test sites including the digestive organs such as the esophagus, stomach, small intestine, large intestine, etc., or the lungs and the like. Moreover, these medical endoscope systems further allow one to apply, as needed, various treatments to the site using a treatment tool inserted through a treatment channel. Particularly in recent years, electronic endoscope systems incorporating as an imaging unit a solid-state imaging element such as a charge coupled device (CCD) have become widely used. The electronic endoscope system can present a motion picture as a monitoring image on a color monitor on a real-time basis. Because of this, the electronic endoscope system is also advantageous in that it exerts less strain on the operator of the endoscope.
The electronic endoscope system comprises an electronic endoscope consisting of a CCD placed at the tip of a slender insertion segment, a processor unit for processing image pickup signals, and a light source apparatus for providing illuminating light. The electronic endoscope can be detachably attached to the processor unit and light source apparatus. Accordingly, for a given electronic endoscope system, it is possible to attach various types of endoscope to a single processor unit and light source apparatus. Further, the electronic endoscope may contain, for example, CCDs having various numbers of pixels depending on the site to which the CCD is applied or for a given application. As for the CCD, the time required for charge reading varies depending on its type.
The CCD installed in the electronic endoscope may include, to reduce the size of its imaging element, a type in which the charge accumulating portion also serves as the charge transferring path. In such a type, the electronic endoscope system must interrupt illuminating light required for illuminating a test object during a period in which the charge of the CCD is read out, so that an image of the object is not formed on the CCD during this period.
An electronic endoscope system which sequentially radiates red, blue, and green light two-dimensionally onto an object to be imaged achieves this by rotating a filter plate in which a light shielding sector is inserted between adjacent color filters. Through this arrangement, the electronic endoscope system based on the sequential two-dimensional light radiation can interrupt the light during light shielding periods. The length of the light shielding period is determined in accordance with the CCD which requires the longest time for charge reading.
For the aforementioned electronic endoscope system, the time required for reading out charge varies depending on the type of solid-state imaging element, such as a CCD, of the imaging unit. Namely, the light shielding period required for an electronic endoscope system varies depending on the solid-state imaging element it employs.
However, the conventional electronic endoscope system has a fixed light shielding period, regardless of the type of electronic endoscope it employs. As a consequence, the conventional electronic endoscope system may have a redundant light shielding period, if it incorporates a solid-state imaging element comprising a small number of pixels in which a relatively short period is required for reading out charge. Consequently, the conventional electronic endoscope system cannot ensure a sufficiently intense light exposure if the test object is in the dark, which has been a problem.